Epitaxial layers are used in a wide variety of devices, including semiconductor devices. In a significant percentage of these devices, a low defect density epitaxial layer is needed for proper device operation. An epitaxial layer is defined as a film that is grown on a substrate having a substrate surface which acts as a seed crystal, wherein the deposited epitaxial film takes on a lattice structure and orientation based on that of the substrate surface.
Crystalline defects are known to include one dimensional, two dimensional and three dimensional defects, which are referred to as propagating defects during epitaxial growth since they propagate in epitaxial layers during epitaxial growth. Such crystalline defects can adversely affect the performance of the device. One-dimensional defects include straight dislocations (edge or screw), dislocation loops, two dimensional defects include grain boundaries stacking faults, & twins, while three dimensional defects include precipitates & voids. In the case of semiconductor devices, during their operation propagating defects can act as scattering centers for carriers, thus reducing carrier mobility which limits the performance (e.g., speed) of the semiconductor device. Propagating defects can also act as centers of non-radiative recombination, affecting performance of light-emitting devices such as light emitting diodes (LED), optical amplifiers, and semiconductor diode lasers. Propagating devices can multiply or transform to other form of defects during device operation and can kill the device or degrade the performance of device (e.g., current collapse or increase reverse leakage current).
Regarding semiconductor integrated circuits (ICs) or semiconductor power devices, wide band gap semiconductors such as gallium nitride (GaN), aluminum nitride, indium nitride and silicon carbide (SiC) along with diamond are sometimes referred as “final frontiers for semiconductors”. For example, group III-nitride semiconductors such as GaN have capabilities including amplifying (with low distortion) high-frequency RF signals, and high temperature operability, and are thus ideally suited for a wide range of applications. GaN is generally grown as an epitaxial layer on a substrate material, such as GaN, SiC, sapphire or Si. One of the most important challenges for rapid development of GaN based RF devices is the ability to control the defect density during GaN epitaxial film growth.
As known in the art, high densities of defects are generally present on the growth template substrates that propagate during GaN film growth process. Although several GaN film growth techniques, such as epitaxial lateral overgrowth (ELOG) process have been developed, the defect density in at least portions of the GaN layer is still very high compared to conventional silicon substrates. Although processes such as ELOG in which the substrate is covered with a patterned SiN or SiO2 masking layer and then selective epitaxial growth occurs from exposed areas on the substrate can significantly reduce the defect density locally, such selective growth processes create regions of varying microstructural quality across the area of the wafer (e.g., high/low defectivity regions) which hinders scalable development of GaN-based devices. There is thus a need to develop new methods and epitaxial articles therefrom that have high quality (i.e. low defect density) across the full area of the epitaxial layer, such as across the full area of the wafer.